Curious to hear your comments on the following:
We don't have a proper process for rescheduling of changes.... or should I say that our process is to cancel the RFC and resubmit (and go through the approval process again). Since CAB meets only once a week and most of our changes are approved by CAB, IT gets annoyed that they have to go through the process again and business units get upset or don't understand why a simple change takes 1-2 weeks to get implemented.

What is a more efficient way of rescheduling of approved changes without putting the business at risk? Some people have suggested contingency dates but that would make the change calendar too confusing (when is the change gonna happen?!?). How do you all handle rescheduling of approved changes?

Hello and welcome, Hena
When an RFC's implementation date changes, you are essentially implementing into a new environment with potentially a whole new set of scheduling issues.
Yes the change is understood, but the CAB must evaluate it in the context of other priorities in the new change window.
It's a matter of educating people.
Hope this helps_________________DYbeach
ITIL V3 Release, Control & Validation,
ITIL V3 Operation SUpport & Analysis
PMI CAPM (R)

"In times of universal deceit, telling the truth will be a revolutionary act." George Orwell

A thorough going review of why changes get rescheduled and an overhaul of the processes to make that much less frequent will do much to quieten the complaints and will qualify as a service improvement initiative.

You can also look at the frequency of CAB meetings. Once a week may well be right, but that implies that the cost of more frequent meetings outweighs the benefits of getting non-urgent changes implemented quicker. I assume that high urgency is catered for separately and that it is realized that rescheduling a change could put it in the high urgency category in some circumstances._________________"Method goes far to prevent trouble in business: for it makes the task easy, hinders confusion, saves abundance of time, and instructs those that have business depending, both what to do and what to hope."
William Penn 1644-1718

... perhaps there are some changes that don't have to go through the CAB and authorization can be given by a Change Manager or they can be made standard changes. I am not familiar with your environment, but this is something potentially to consider to reduce wait time. Be careful though to make sure that all risks are carefully considered and nothing is bypassed for the sake of speedier processing of changes.

I would be looking at the IT department that is to make the change asking, why has the change implementation date been missed?
The management of IT teams is key to ensure that approved changes are actioned to the date as recorded on the RFC.
Your cab should contain the managers and/or team leaders from the area of IT that is to make the change,they will see that the change has been approved along with the date the change is to be implemented._________________Change Management
"Bringing order to chaos"